As the Washington Nationals start their exhibition games, when rookies dot the lineup and vets try to hide how tickled they are to be back playing baseball, they might want to consider one thought that is as cold as ice.

Year after year the Caps said, as the Nats are now saying for the third straight year, we have the talent, we have what it takes, right here in this room, to play for a championship. Our window of opportunity is wide open.

Right up until it isn’t. Alex Ovechkin is in his ninth season. Nine. Even with the three-time MVP on pace to score nearly 58 goals, the Caps are 16th in the NHL in points and have a coin-flipper’s chance at the playoffs.

They are no longer one of the six or eight teams that is in Stanley Cup debates. They’re just a decent back-in-the-pack team, outscored this year, with a puncher’s chance to find a hot goalie in the playoffs, get their lines right, fall into a couple of advantageous early-round matchups and . . .

And be what? A miracle team? Great, love to see it. Only four months ago we enjoyed the last such team in a major sport — the last-place-to-World-Series-winning Red Sox. Such fun actually does happen. But it has nothing to do with open windows. That’s what the Nats should understand.

If the Caps had made horrid mistakes, the pain of watching them now as they struggle to be average would not be so annoying and poignant. But they didn’t. Their exceptionality just slipped away as the years sped past.

The Caps should illustrate to the Nats that you don’t have to be a farce franchise run like the FedEx football circus to disappoint your dreams. Everybody from the owner to the Zamboni driver can be pretty good and extremely conscientious. And the result can still be “no dice.”

Perhaps one message is clear as you try to climb through that window: Look honestly and critically at what is happening to you. That may not be enough. But it’s essential. The Caps never did, at least not in public.

When the Caps failed, the coaches, the general manager and the owner, who always sets the tone, apologized for the team, covered for them and said, “Next year.” What you never heard was: When this much ability produces so little in the playoffs, then something is significantly wrong. As a result, the Caps returned each season, saying the right things but never with raw urgency. There’s a high price for being even slightly self-deluded.

Will the Nats do better at facing facts? In 2012, they blew a 6-0 lead in a game that would have taken them to MLB’s final four. They were young. Hindsight says St. Louis was better. Understandable, just like the early Caps exits. But you have to say, “That’s one.”

Then last year, the Nats played tight for months. The Braves beat them repeatedly with mental toughness and fundamentals. “Expectations” got the Nats, an old baseball disease. It was hard to believe, much like the Caps’ Game 7 loss at home to eighth-seeded Montreal in 2010. But after you smack your forehead, here’s what else you say if you’re the Nats: “That’s two.”

It’s true the Nats have a lot of key players under team control for a lot of years, plus an impressive stampede of pitchers in the minors. That’s the kind of accurate but too-cheerful talk that often distracted the Caps. The Nats count all their “great young arms” like the Caps counted their young talent. It sounds logical, unless few of them prove exceptional.

Here’s the quick and dirty: Don’t hate the Caps, but don’t become them.

The Nats can only be absolutely sure that their window will stay wide open for two more years. After that, Jordan Zimmermann or Ian Desmond or both could leave as free agents. For now, neither seems to be leaning toward accepting any hometown discount to stay, and teams are crazy to issue full-price $100 million career insurance policies two years before free agency to players who are very good but aren’t going to the Hall of Fame.

After 2016, Stephen Strasburg can be a free agent. The large majority of Scott Boras’s top clients change teams for top dollar as early as possible. By the time a player leaves high school, he knows who he is, what he wants. His agent is his tell. The Lerners smile. They know better. They’ll stay with us. Okay, but make sure you have Lucas Giolito ready for opening day of ’17.

When teams are very good and might soon be great, everybody’s happy from the anticipation. Few want to nag. But you can end up living in a sports echo chamber where you seldom hear anything that’s not welcome, especially if you are the most talented players or the bosses.

What don’t the Nats want to hear? They have ability, but it’s not fully polished, especially Strasburg and Bryce Harper. Their work ethic and maturity off the field appears to be exemplary. It’s on the field that they are sometimes immature. The last two years Davey Johnson made their world less prickly by interpreting them generously to the public with his humor. The Caps coddled some of their young guns off the ice. The Nats need to make sure that they are candid — not cruel but direct — about on-field flaws in their young talents or their demeanor under adversity. They can take it.

Finally, the Nats have owners who keep learning but perhaps not as fast as they think. When their baseball people handed them two industry-praised trades — for Gio Gonzalez and Doug Fister — they balked both times and required days of debate before signing off. If good people do fine work and it’s not recognized, one day they’re gone.

When the Nats give a $125 million contract, that’s Ted Lerner’s money. But when scouts, coaches, stats analysts and an entire front office discover, draft and develop minor league players, then deliver a prospects-for-a-star trade, the owner’s job is to know how little he knows and say, “Great work!”

The Nats’ window now, like the Caps’ for many years, appears to be invitingly open. That means if many things go right and not too much goes wrong, the Nationals may one day just barely squeeze through it.

Thomas BoswellTom Boswell has been a Washington Post sports columnist since 1984. He started at The Post in 1969 as a copy aide, and he spent 12 years as a general-assignment reporter, covering baseball, golf, college basketball, tennis, boxing and local high school sports. Follow